table: Add --max-column-width option.

This can make it easier to read tables that contain wide data in some
columns.

Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Justin Pettit <jpettit@ovn.org>

NEWS

@@ -8,6 +8,8 @@ Post-v2.8.0
      * ovsdb-client: New "get-schema-cksum" and "query" commands.
      * ovsdb-client: New "backup" and "restore" commands.
      * ovsdb-tool: New "db-name" and "schema-name" commands.
+   - ovs-vsctl and other commands that display data in tables now support a
+     --max-column-width option to limit column width.
    - OVN:
      * The "requested-chassis" option for a logical switch port now accepts a
        chassis "hostname" in addition to a chassis "name".

lib/table.c

@@ -255,19 +255,31 @@ table_print_table__(const struct table *table, const struct table_style *style)
         puts(table->caption);
     }
 
-    widths = xmalloc(table->n_columns * sizeof *widths);
+    widths = xzalloc(table->n_columns * sizeof *widths);
     for (x = 0; x < table->n_columns; x++) {
         const struct column *column = &table->columns[x];
 
-        widths[x] = strlen(column->heading);
+        int w = 0;
         for (y = 0; y < table->n_rows; y++) {
             const char *text = cell_to_text(table_cell__(table, y, x), style);
             size_t length = strlen(text);
 
-            if (length > widths[x]) {
+            if (length > w) {
-                widths[x] = length;
+                w = length;
             }
         }
+
+        int max = style->max_column_width;
+        if (max > 0 && w > max) {
+            w = max;
+        }
+        if (style->headings) {
+            int min = strlen(column->heading);
+            if (w < min) {
+                w = min;
+            }
+        }
+        widths[x] = w;
     }
 
     if (style->headings) {
@@ -295,7 +307,7 @@ table_print_table__(const struct table *table, const struct table_style *style)
             if (x) {
                 ds_put_char(&line, ' ');
             }
-            ds_put_format(&line, "%-*s", widths[x], text);
+            ds_put_format(&line, "%-*.*s", widths[x], widths[x], text);
         }
         table_print_table_line__(&line);
     }

lib/table.h

@@ -78,21 +78,24 @@ struct table_style {
     enum cell_format cell_format; /* CF_*. */
     bool headings;              /* Include headings? */
     int json_flags;             /* CF_JSON: Flags for json_to_string(). */
+    int max_column_width;       /* CF_STRING: Limit for column width. */
 };
 
-#define TABLE_STYLE_DEFAULT { TF_LIST, CF_STRING, true, JSSF_SORT }
+#define TABLE_STYLE_DEFAULT { TF_LIST, CF_STRING, true, JSSF_SORT, 0 }
 
 #define TABLE_OPTION_ENUMS                      \
     OPT_NO_HEADINGS,                            \
     OPT_PRETTY,                                 \
-    OPT_BARE
+    OPT_BARE,                                   \
+    OPT_MAX_COLUMN_WIDTH
 
 #define TABLE_LONG_OPTIONS                                      \
         {"format", required_argument, NULL, 'f'},               \
         {"data", required_argument, NULL, 'd'},                 \
         {"no-headings", no_argument, NULL, OPT_NO_HEADINGS},    \
         {"pretty", no_argument, NULL, OPT_PRETTY},              \
-        {"bare", no_argument, NULL, OPT_BARE}
+        {"bare", no_argument, NULL, OPT_BARE},                  \
+        {"max-column-width", required_argument, NULL, OPT_MAX_COLUMN_WIDTH}
 
 #define TABLE_OPTION_HANDLERS(STYLE)                \
         case 'f':                                   \
@@ -115,6 +118,10 @@ struct table_style {
             (STYLE)->format = TF_LIST;              \
             (STYLE)->cell_format = CF_BARE;         \
             (STYLE)->headings = false;              \
+            break;                                  \
+                                                    \
+        case OPT_MAX_COLUMN_WIDTH:                  \
+            (STYLE)->max_column_width = atoi(optarg); \
             break;
 
 void table_parse_format(struct table_style *, const char *format);

lib/table.man

@@ -69,3 +69,8 @@ This option does not affect JSON in tables, which is always printed
 compactly.
 .IP "\fB\-\-bare\fR"
 Equivalent to \fB\-\-format=list \-\-data=bare \-\-no\-headings\fR.
+.IP "\fB\-\-max\-column-width=\fIn\fR"
+For table output only, limits the width of any column in the output to
+\fIn\fR columns.  Longer cell data is truncated to fit, as necessary.
+Columns are always wide enough to display the column names, if the
+heading row is printed.